Currently, _replicateSearchIndexCommandOnAllMongodsForTesting supports creating a search index for sharded collections and untracked unsharded collections in a sharded cluster. However, it's also possible that a collection can be unsharded but tracked (e.g. after a moveCollection). We should also support the helper in this case - we should be able to call getAllShardIds() to get the shards that own chunks, which should just be one shard for tracked unsharded collections, and set targetHosts to that shard.